The present invention relates generally to satellite communications terminals and more particularly to very small aperture terminal (VSAT) outdoor unit (ODU) communications equipment. VSAT remote terminals can be used to receive or communicate data, voice and video, from or to a central hub via a satellite. Typically, the VSAT remote terminals have a small aperture directional antenna for receiving from or transmitting signals to a satellite, the ODU mounted near the antenna for transmitting a modulated carrier, and an indoor unit (IDU) for generating the modulated carrier. The ODU is connected to the IDU with an IFL cable for transmitting signals between the ODU and IDU and for providing DC voltage to the ODU. The IDU also demodulates incoming signals received from the ODU and operates as an interface between a user""s communication equipment and the ODU.
To install a VSAT remote terminal, the IDU is connected to the ODU with IFL cable. An installer then aims the directional antenna. The installer connects a voltage meter to an antenna pointing connector on the ODU. As the antenna is aimed towards the satellite, the IDU receives a signal from the satellite. A pulse width modulated signal is generated in response to the receipt of the satellite signal and output at the antenna pointing connector. The rate of the pulse width modulated signal is sufficiently high to allow the volt meter to measure an average DC voltage. As the antenna is aimed more accurately, the averaged DC voltage will decrease. Once the antenna is aimed, the installer goes indoors and attempts to transmit to the satellite from the IDU.
A transmission circuit is located in the ODU. To properly transmit, the transmission circuit needs a certain level of input DC voltage. A faulty or improper IFL cable will not provide sufficient input DC voltage to the ODU. The cable may be faulty or improper due to defects in a particular cable, improper selection of a cable resistance and/or cable length. A low voltage detection circuit in the ODU will disable the transmission circuit if the input DC voltage is too low.
Generally, there are two types of transmission circuits for use in an ODU. The first type is the intelligent transmission circuit. The intelligent transmission circuit has a processor for operating phase-shift keying circuitry, linear upconverters and a linear power amplifier. The processor is capable of detecting the input DC voltage and communicating with the IDU over the IFL cable. For instance, the ODU processor could inform the IDU that the DC voltage input is not high enough for proper transmission to the satellite. Thus, the installer would know to check the cable for irregularities. However, the installer would not know of this problem until after going indoors to the IDU.
The second type of transmission circuit is a non-intelligent or xe2x80x9cdumbxe2x80x9d transmission circuit. xe2x80x9cDumbxe2x80x9d means the transmission circuit does not communicate with the IDU. Typically, the dumb transmission circuit has a phase-lock loop, frequency multiplier and a saturated amplifier. The dumb transmission circuit cannot inform the IDU that the DC voltage input is not high enough for proper transmission. The installer then unsuccessfully attempts to transmit. The installer does not know that the cable is faulty, believes the VSAT remote terminal is faulty and returns the VSAT remote terminal to the manufacturer.
Therefore, there is a need for a system and method for informing the installer that the cable is faulty. Further, there is a need for a system and method for informing the installer that the cable is faulty at the ODU.
The present invention provides an outdoor unit of a remote terminal designed to satisfy the aforementioned needs. Specifically, the present invention provides a novel design for the remote ground terminal that informs the installer at the ODU that the cable is faulty.
Accordingly, the present invention relates to a VSAT communications outdoor unit for satellite communications. The outdoor unit comprises a dumb transmission circuit and a voltage detection circuit. A signal generator operatively connects to the voltage detection circuit and is responsive to the voltage detection circuit. In one embodiment, the dumb transmission circuit comprises a saturated amplifier, and the signal generator comprises a low frequency oscillator for outputting a low frequency signal to an antenna pointing connector.
In another aspect of the invention, a VSAT communications outdoor unit for satellite communications is provided. The ODU comprises a transmission circuit and a voltage detection circuit. A signal generator responds to the output of the voltage detection circuit. An external output connects to the signal generator.
The present invention also relates to a method for indicating that a cable is malfunctioning in a VSAT communications remote terminal. The method comprises the steps of detecting in an outdoor unit an insufficient DC voltage to operate a transmission circuit and indicating with an external output that the transmitter is disabled. The external output is separate from a link to the indoor unit.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. The invention, together with further objects and attendant advantages, will be best understood by reference to the following detailed description in conjunction with the attached drawings.